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What is obesity?

Scientific support: Theresa Kössler

Obesity is a term to describe being severely overweight. Obesity is also referred to as adiposity.

Obesity is not only a cosmetic issue, but rather a chronic disease that can be accompanied by serious health problems. For example, it is a risk factor for the onset of type 2 diabetes, cardiovascular disease, and certain types of cancer.

In Germany, 67 percent of men and 53 percent of women are overweight. Roughly one-quarter of them are considered obese.

1. How does obesity develop?

Obesity develops when energy intake is greater than energy expenditure. This is usually the result of too much food and not enough physical activity. In the long term, even a small imbalance between energy intake and expenditure can result in weight gain and eventually obesity.

Alongside lifestyle, genetic and psychological factors play an important role in the onset of obesity.

2. What increases the risk of obesity?


A number of factors can facilitate the development of obesity:

  • High incidence of obesity in the family
  • Unhealthy lifestyle
    • Lack of physical exercise
    • Eating large portions and the constant availability of high-energy foods
    • High-calorie foods
    • A low-fiber and/or high-fat diet
  • Stress, depression, and lack of sleep
  • Eating disorders
  • Metabolic diseases (for example, hypothyroidism or Cushing's syndrome)
  • Medications that can affect body weight (for example, cortisone and some drugs used to treat depression, high-blood pressure, or diabetes)

3. How is obesity diagnosed?

The body mass index (BMI) is a measure to assess body weight in relation to height. The result is obtained by dividing body weight (kg) by height squared (in m²).

A BMI between 18.5 and 24.9 kg/m² is considered normal. A BMI of 25 kg/m² or above is considered overweight. Someone is considered obese when their BMI is 30 kg/m² or above.

    Good to know:

    The formula to calculate the body mass index (BMI):

    BMI = body weight (kg) : height squared (m²)

    The greater the BMI, the greater the risk of developing other diseases.


    Body mass index (BMI) [kg/m²]

    Risk of complications


    Below 18.5


    Normal weight

    18.5 to 24.9



    25 to 29.9

    Slight increase


    Above 30


         Class 1

    30 to 34.9


         Class 2

    35 to 39.9


         Class 3

    Above 40

    Very high

    However, body weight is not the only decisive factor for the risk of developing complications. The distribution of fat in the body also plays an important role. A high accumulation of abdominal fat is associated with a higher health risk. The amount of abdominal fat can be determined by measuring the circumference of the waist.

    There is a significantly elevated risk of metabolic and cardiovascular diseases

    • in women with a waist circumference of 88 centimeters or more
    • and men with a waist circumference of 102 centimeters or more.

    4. How can obesity be prevented?

    There are several measures that can help prevent weight gain and obesity. Lifestyle in particular plays a crucial role:

    • Try to have a balanced and fiber-rich diet.
      Avoid energy-rich food containing unhealthy fats and added sugars. For example, soft drinks, sweet snacks, fast food, and fatty processed meats. At the same time, increase your intake of foods with a low energy density, such as vegetables, fruit, and wholegrain products.
    • Try to give up alcoholic drinks as much as possible.
    • Try to exercise regularly and integrate physical activity into everyday life.

    Good to know:

    Helpful tips for a healthy and balanced lifestyle can be found by clicking on the menu items "What can I do?" and "How do I motivate myself?".

    5. What are the health risks associated with obesity?

    Obesity can lead to a range of health-related problems and severely affect quality of life. There is hardly an organ or organ system that is not affected by diseases associated with obesity.

    The close correlation between body weight, or waist circumference, and the risk of type 2 diabetes is worthy of particular mention. The duration and severity of obesity play a decisive role: For every 1 kg/m² increase in BMI, the risk of type 2 diabetes increases by 20 percent.

    You can find more information about the onset of type 2 diabetes here!

    Good to know:

    Obesity comes with a higher risk of diabetes.

    As a general rule: The longer someone is overweight and the more severe their condition is, the more difficult it is to treat and the more obesity-associated complications arise. In certain cases, the potential complications cannot be reversed.


    6. How can obesity be treated?

    The main aims of obesity therapy are:

    • Long-term body weight reduction
    • Therapy and prevention of the complications associated with obesity
    • Improving quality of life

    To ensure the greatest possible success, the treatment must be realistic and tailored to individual requirements. Even losing 5 to 10 percent of body weight can have a positive effect on health.

    It is also important to achieve long-term weight control beyond the weight loss phase.

    Good to know:

    A 5 to 10 percent loss of the initial body weight can improve health.

    Weight loss is recommended for following people:

    • Obese people with a BMI of 30 kg/m² or above.
    • Those who are overweight with a BMI score between 25 and 29.9 kg/m², who also
      • suffer from other diseases, such as high blood pressure or type 2 diabetes,
      • abdominally-centered fat distribution with a waist circumference exceeding 88 (women) or 102 cm (men) or
      • are subject to increased psychosocial stress.


    The basic obesity treatment program is based on 3 pillars. Diet, exercise, and behavior.


    The body must take in less energy than it uses to enable weight loss. Energy intake should be approximately 500 kilocalories (abbreviated as kcal, commonly known as calories) below the actual daily requirement. This makes continuous weight loss of around 1 to 2 kg per month achievable.

    It doesn’t matter if the reduced energy intake is the result of a decrease in the intake of fat, carbohydrates, or a combination of both. It is important that a dietary form is selected that suits you and is sustainable in the long term. Care should also be taken to ensure that the body continues to receive all the essential nutrients.

    Find out more about a balanced diet!


    Physical activity leads to increased energy consumption and prevents loss of muscle mass. This has positive effects on weight reduction and stabilization.

    Furthermore, regular physical activity has beneficial effects for health and quality of life.

    Read here about how physical activity affects health!

    The target is at least 150 minutes of physical activity per week. Endurance sports, such as hiking, walking, jogging, cycling, or swimming are ideal. The type and intensity of the physical activity should be tailored to individual health status and preferences. Most importantly, the exercise should be fun!

    Here, you can find useful tips to get motivated and start exercising!

    You should also try to integrate more movement into your everyday routine. There are numerous ways to do this, for example:

    • Take the stairs instead of the elevator.
    • Choose to walk short distances instead of taking the car, tram, or bus.
    • Take a relaxing walk in the evening.
    • Place devices often needed for work out of reach.


    Alongside diet and exercise, your own behavior plays a crucial role in the treatment of obesity. It is often necessary to adjust previous lifestyle habits in order to reduce weight and maintain it over the long term. Participation in behavioral therapy can be very helpful in achieving this goal.

    Other treatment options

    If the basic program results in no or little weight loss, drug-based or surgical measures can be used in the treatment of obesity.

    However, these treatment options are associated with potential side effects and risks and should only be considered when the conservative therapy options have been fully exhausted and

    • in case of extreme obesity, or
    • if the patient is severely overweight and has complications, such as type 2 diabetes or high blood pressure.


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    Deutsche Diabetes Gesellschaft et al.: Deutscher Gesundheitsbericht Diabetes 2020. Kirchheim Verlag, Mainz, 2020
    Hauner, H. et al.: Adipositas und Diabetes mellitus. In: Diabetologie, 2018, 13: 192-198
    Hauner, H.: Ernährungsmedizinische Konzepte bei Adipositas. In: Internist, 2015, 56: 137-142
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    As of: 09.01.2020